We've toyed with taglines at the top and once the iPhone app/Android app were done we wanted to use that space to advertise. We definitely need to work something short back in there.

We have a few different ideas for monetization; the most obvious one is auctioning off that 'hot tweet' area on a nightly basis; that is seen by every web/mobile user. I like it because these are advertisements our users would actually want to see.